Switching-induced transient overvoltages are a common problem in high-speed, high power switching circuits, such as switching power converters and pulse modulators. Rapid current or voltage changes during commutation generate transient voltages because of the energy stored in circuit inductances and capacitances. In modern high-power switching circuits where current and voltage slew rates can reach 1 kA/ xcexcs and 10 kV/ xcexcs, transient voltage spikes can be quite severe. A number of voltage transient suppression circuits and devices have been developed in an attempt to solve this problem.
It is known to use a capacitive xe2x80x9csnubberxe2x80x9d as a voltage transient suppression circuit. A xe2x80x9csnubber circuitxe2x80x9d is shown in FIG. 1 generally at 10 (comprising a resistor 12 and capacitor 14 wired in series) in parallel with a switching power semiconductor 16. The resistor 12 and the capacitor 14 together form the snubber circuit 10, which is used in many different applications to limit the voltage overshoot and the rate of change in the voltage when a transient occurs in the system. A sudden rise in voltage across a switching power semiconductor 16 opening will be tempered by the charging action of capacitor 14 (the capacitor 14 opposing the increase in voltage by drawing current). During ON/OFF transition, the capacitor 14 is being charged by absorbing the energy stored in circuit inductance 17. The resistor 12 limits the amount of current that the capacitor 14 will discharge through the switching power semiconductor 16 when it closes again. The capacitor 14 is discharged during the ON state of the switching power semiconductor 16. Stored energy in capacitor 14 dissipates during the next ON period in resistor 12 and in the switching power semiconductor 16. Although the operation of each of the various snubbers differs slightly from the others, the method employed by all of the snubbers to suppress transient voltage is similar.
These snubber circuits, while generally able to limit voltage transients to a desirable level, have several disadvantages. For example, one disadvantage of this snubber circuit is that, due to the typical nature of its function, the resistor is sized such that it can withstand the power applied when the capacitor is working properly, but the resistor would have significantly more than its rated power applied to it if the capacitor fails or is shorted. In a typical circuit, when the capacitor shorts, the resistor power dissipation can be 100 times higher than its rating. Consequently, if the capacitor fails, the resistor will fail catastrophically shortly afterward. It is usually undesirable to select the resistor power rating to continuously withstand shorted capacitor conditions due to cost and mechanical constraints. Also, in many applications, a mechanism to detect capacitor failure and remove power cannot act quickly enough to protect the resistor. Attempts to implement a faster detection circuit often result in false triggers due to noise, which adversely impact the equipments reliability. Thus, there is a desire to eliminate the possibility of catastrophic resistor failure should the capacitor fail in a snubber circuit, while still providing a reliable, cost effective, and mechanically practical power circuit design.
The above discussed and other drawbacks and deficiencies are overcome or alleviated by a voltage transient suppression circuit for power electronic circuits comprising: a snubber circuit having a resistor and a first and second capacitive element connected in series with a resistive circuit element; and a sensing logic device connected in parallel with the snubber circuit. The logic circuit is configured to receive voltage signals indicative of said first and second capacitive elements of the snubber circuit, and said logic circuit utilizes said voltage signals to determine if a component failure has occurred.